The present invention relates to a grease composition for a constant velocity joint or a fixed type joint and slide type joint.
In general, a combination of a fixed type joint, a shaft and a thrust type joint is employed when a constant velocity joint is applied in FF type or front wheel driven type cars.
Examples of fixed type joints include Birfield joints, Rzeppa joints, undercutting free joints and tripod joints. Examples of slide type joints include double off-set joints, tripod joints and closs groove joints.
Constant velocity joints are generally lubricated with an extreme pressure grease made up of a base grease consisting of a purified mineral oil, a lithium soap and an urea thickner which is combined with molybdenum disulfide, a sulfur-phosphorus compound, a lead compound, etc.
In the grease composition for the constant velocity joint, there are required characteristics such as anti-flaking, anti-seizure, abrasion resistance or low friction properties. However, there are tendencies to high performances and high quality of an automobile so that the conventional grease compositions are generally lacking in these areas. In particular, in the view of a prolonged life time of the constant velocity joint, it has been desired to improve the anti-flaking performance. Flaking means structural destruction occurring within the interior of metal, which is totally different from seizure occurring on metal surfaces. With the conventional extreme pressure agents, flaking has not been fully avoided.